Lesson xxv.] LIGHT AND cotouus. 159 



stars : 2. Those which transmit the rays, as the 

 air, and glass : and 3. Those which rt fleet them, 

 as the moon, the earth, polished iron, &c. The 

 first are called luminous, the second p llucid, and 

 the third opaque bodies. Ii is also to be observed, 

 that the rays of Light themselves are not seen ; but 

 by their means we see the luminous bodies, from 

 which thi-y originally came, and the opaque bodies, 

 from which they are reflected thus, for instance, 

 when the moon shines, we cannot see the rays 

 which pass from the sun to the moon ; but, by their 

 means, we see the moon, from whence they are 

 reflected. If the eye be placed directly in the me- 

 dium, through which the rays pass to it, the me- 

 dium is notseen ; thus, we never see the air through 

 which the rays come to our eyes. But if a pellucid 

 bodv, through which the rays are to pass, be placed 

 at a distance from our eyes, that body will be 

 seen, as well as those bodies from whence the rays 

 come which pass through it to our eyes. For in- 

 stance, he who looks through a pair of spectacles, 

 not only sees bodies through them, but -also sees 

 the spectacle glasses; because the glass, being a 

 solid body, reflects some rays of light from its sur- 

 face; and being placed at a convenient distance 

 from the eye, may be seen by those reflected rays, 

 at the same time lhat bodies at a greater distance 

 are rendmd visible by the transmitted rays. 



The properties, of reflection and refraction pro- 

 duce several curious effects, some of which have 

 been noticed in the Sixteenth Lesson ; and others 

 will be spoken of as we proceed. 



Amongst 



